You're kind of stuck, aren't you. At 13, you're dependent on parents for transportation, so that lets out a lot of ideas. It's especially hard to meet people in your age group while school's out of session, and I recall that at that age, a single year difference can make a lot of difference.
I would suggest you persue your own interests, whatever they are, and kind of keep an eye out for opportunities. Otherwise, I don't have any ideas, but maybe I can bump up the question and see who jumps in.
We have several mothers here with kids your age, and they've hit just about everything that could come along.